Write valid Scheme functions for the following problems:

$($a$)(4$ points$)$ The predecessor function for a given integer intnum.

$($b$)(4$ points$)$ The successor function for a given integer intnum.

$($c$)(4$ points$)$ The functions odd? and even?, that returns the boolean True if the integer number provided is respectively, odd or even. It should return False otherwise. Functions odd? and even? should be mutually recursive.